我在StackOverflow上测试了一个代码块来评论这里,我遇到了隐式接口变量触发它的情况。我无法看到的是在这种情况下导致它的原因。我有一个小工厂返回一个新创建的对象的接口。如果我在过程块中调用方法,那么我只能得到1的引用计数。如果我从主程序块中调用它,那么我得到的引用计数为2.什么时候Delphi编译器创建一个隐式接口变量?
我使用Delphi 10 Seattle进行了测试。是否存在包含隐式接口创建规则的资源,并且工厂返回的接口不是可靠模式?
program TestRefCount;
{$APPTYPE CONSOLE}
{$R *.res}
uses
System.SysUtils,
Vcl.Dialogs;
type
IMyInterface = interface(IInterface)
['{62EB2C46-9B8A-47CE-A881-DB96E6F6437D}']
procedure DoSomething;
function GetRefCount: Integer;
end;
TMyObject = class(TInterfacedObject, IMyInterface)
strict private
FMyValue: Integer;
public
procedure Init;
procedure DoSomething;
function GetRefCount: Integer;
end;
TMyFactory = class(TObject)
private
function CreateMyInt: IMyInterface;
end;
procedure TMyObject.DoSomething;
begin
MessageDlg(IntToStr(FMyValue), mtInformation, [mbok], 0);
end;
function TMyObject.GetRefCount: Integer;
begin
Result := FRefCount;
end;
procedure TMyObject.Init;
begin
FMyValue := 100;
end;
function TMyFactory.CreateMyInt: IMyInterface;
var
myObject: TMyObject;
begin
myObject := TMyObject.Create;
Assert(myObject.GetRefCount = 0);
myObject.Init;
Assert(myObject.GetRefCount = 0);
Result := myObject;
Assert(myObject.GetRefCount = 1);
Assert(Result.GetRefCount = 1);
end;
procedure WorkWithIntf;
var
myFactory: TMyFactory;
myInt: IMyInterface;
begin
myFactory := TMyFactory.Create;
try
myInt := myFactory.CreateMyInt;
Assert(myInt.GetRefCount = 1);
myInt.DoSomething;
Assert(myInt.GetRefCount = 1);
finally
myFactory.Free;
end;
end;
var
myFactory: TMyFactory;
myInt: IMyInterface;
begin
try
// This case doesn't have an implicit interface variable
WorkWithIntf;
// This case does have an implicit interface variable
myFactory := TMyFactory.Create;
try
myInt := myFactory.CreateMyInt;
Assert(myInt.GetRefCount = 1); // This fails because the refcount is 2
myInt.DoSomething;
Assert(myInt.GetRefCount = 1);
finally
myFactory.Free;
end;
except
on E: Exception do
Writeln(E.ClassName, ': ', E.Message);
end;
end.
下面是其中不存在隐式接口变量第一块:
TestRefCount.dpr.67: myInt := myFactory.CreateMyInt;
005C6A5A 8D55F8 lea edx,[ebp-$08]
005C6A5D 8B45FC mov eax,[ebp-$04]
005C6A60 E83BFEFFFF call TMyFactory.CreateMyInt
TestRefCount.dpr.68: Assert(myInt.GetRefCount = 1);
005C6A65 8B45F8 mov eax,[ebp-$08]
这里是第二块,其中我们可以看到隐式接口变量:
TestRefCount.dpr.86: myInt := myFactory.CreateMyInt;
005CF513 8D55EC lea edx,[ebp-$14]
005CF516 A19CB75D00 mov eax,[$005db79c]
005CF51B E88073FFFF call TMyFactory.CreateMyInt
005CF520 8B55EC mov edx,[ebp-$14]
005CF523 B8A0B75D00 mov eax,$005db7a0
005CF528 E8C7E3E3FF call @IntfCopy
TestRefCount.dpr.87: Assert(myInt.GetRefCount = 1); // This fails because the refcount is 2
005CF52D A1A0B75D00 mov eax,[$005db7a0]